Device and cathode-ray tubes for stabilising high voltages



July 8, 1958 s. VAN DER MEER A DEVICE AND CATHODE-RAY TUBES FOR STABILISING HIGH VOLTAGES Filed Dec. 9, 1954 2 Sheets-Sheet 1 I'l I l INVENTOR SIMON VAN DER MEER AGENT y 1958 s. VAN DER MEER 2,842,710

DEVICE AND CATHODE-RAY TUBES FOR STABILISING HIGH VOLTAGES Filed Dec. 9, 1954 2 Sheets-Sheet 2 6 I V0 i 2! K MN. -18 la W Hu NW SIMON VAN DER MEER AGENT path between the pole-pieces. to be stabilised may be maintained constant by controlling undesirable extent.

' Use is preferably made of a permanent magnet having tat ' DEVICE AND CATHGDE-RAY TUBES FO R STABILISING HHGH VULTAGES Simon van der MeenEindhoven, Netherlands, assignor,

' by mesneassignments, to NorthA-merican hilips Com= pany, Inc., New York, N. Y., a corporation of Deia ware Application December 9, 1954, Serial No. 474,174 Claims priority, application Netherlands January 22, 1954 l 4 Claims. (Cl. 315-) .tions in voltage having to be smaller than, for example,

0.05%. Such is the case inter alia in electron-diitraction apparatus, micro-analysers, X-rayapparatus and the like. Such devices usually operate at voltages of kilovolts and higher. I

It is known to stabilise the voltage of an electron microscope with the use of a cathode-ray tube, of which the ray of electrons extends between two parallel pole-pieces of an electromagnet, thus traversing an angle of about 90. The velocity of the electrons and hence the curvature'of the path of electrons between the pole-pieces is dependent upon the voltage to "be stabilised. If this voltage increases, the electrons are accelerated toia greater extent, resulting in a greater radius 'of curvaturebf the The 'value of the voltage this voltage manually or automatically in such manner that the curvature of the path is maintained constant in that, for example, a luminous point produced by the ray 7 on a fluorescent screen is maintained at a determined area.

However, such a device is in many cases not sufficiently sensitive for the above-mentioned purposes.

The voltage may be readjusted automatically, for example, with the use of a device as described in Physical Review, vol. 70, pages 8844585, in which deviations of the beam' from its normal position result in variations in the current distribution over a pair of collector plates.

Said current variations, after being amplified, serve to control the high voltage.

A satisfactory stabilisation which aifords material ad vantages in regard to sensitivity'and structure may be obtained .byproviding a device for stabilising high voltages comprising a cathode-ray tube inwhich a ray of electrons is deflected in a constant magnetic field comprising regions of great field strength and adjoining regions of smaller field strength. The curvature of the'pa'th of electrons is dependent upon the voltage to be stabilised, which ray of electrons partly strikes a. collector electrode if the voltage to be stabilized has the correctvalue, the

,. variations in the current to the said electrode serving'to control the voltage to be stabilized. According to the invention, at the correct value of the voltageto be stabilized,'the beam extends at least through part' of its path in the vicinity of, and substantially in .parallel with, the transition zone between a region of'great field strength and a region of smaller field strength, whereby'the part of the ray of electrons striking the collector varies and strength if the voltage to be stabilised increases to an polepieces in the form of semi-circular discs. By pro the ray at the same time enters a region of smaller-field- Patented July 8, 1958 ing viding opposinggroovesin the adjacent-surfaces of the poles, it is possible to obtain regions of different field strength, between which the field strength exhibits a high gradient, sinc e at the grooves the spacingbetween the pole surfaces is greater than at the other areas. By providing different grooves which are required to extend in parallel with the lastpart of a corresponding path of electrons, it is possibleto utilize the device for different voltages. semi-circular disc-shaped pole-pieces, between which the ray of electrons enters tangentially and describes an arc a of, say, in parallel with the curved edges of the poles to strike at last the edge of a collector electrode;

A high sensitivity is obtained owing to the-particulararrangement according to the invention, since in thecase of an unwanted increase in the voltage to be stabilized, as a result of which the velocity of the electrons in the ray and hence-also the radius of the path of electrons between the pole-pieces increases, this increase in radius becomes even higher due to the ray of electrons, which is in a field strength of high gradient, moving towards the adjoining region of smaller field strength. Consequently, comparatively small deviations from the voltage to be stabilised can bring about comparativcly great variations in the curvature of the path of electrons and hence in the cur- The variations in the companying drawings, {given by way of example, in which Figs. 1 and 2 show a determined embodiment of a tube for use in a device according to the invention. i

Fig. 3 shows a curve.

Figs. -4 and 5 show details of another embodiment and Fig. 6 shows a curve corresponding to the embodiment of Figs. '4 and 5."

In Fig. '1, reference numeral '1 indicates the bulb of respec= a tube closed at its extremities by bases 2 and 3 tively, in which contact .pins 4 are sealed.

The tube contains an electron gun 5 whichhouses a cathode 6, the "construction being such that the voltage to be stabilised, which is from 30 to 5.0 kilovoltsand upwards, may be connected directly between the cathode 6 and ananode 7. The velocity of the electrons leaving the gun in the form of a thin ray is thus directly dependent upon the voltage .to be stabilised; The ray of .electrons extends through an--aperture of anode .7 to enter-tangentially between magnet poles 8 and '9. The poles .8 and 9 are secured to ironplates 1-0 .andll .(Fig. 2) between which a permanentmagnet l2,'whose polarity is indicated by letters N, andS representing the north and south poles, is clamped in' position, nected to theanode-Tby'rneansof asupporting plate.

The rayof electrons. between the poles Sand 9 describes a curved path which, accordingtojhe invention; extends just along the outer edges of themagnet poles wherethe gradient of the field strength is high, if the voltage to be stabilised has the'desired'value'v After leaving thespace between thepolepiecea the ray partly strikes the edge of acollect'o'r electrode 151; impinge inypart via the said edge upon a screen 14 which is connected to anode 7 and which prevents the glass of the bulb. '1 from being .struck .byelectrons. If the voltagev to. be stabilised slightly .increasesg'the radius of the pathof electrons'rincreases, which increase is enhancedjdue to the electrons reaching'aregion of smaller field strength;

in the simplcstembodiment use is made of The plates 10 and 11 are con-' viz. outside the edges of the pole-pieces. Since the edge of the collector electrode 13 is exactly opposite the edges of pole-pieces 8 and 9, a larger proportion of the ray of electrons thus extends along the said electrode.

The operation of the tube follows from Fig. 3, in which the voltage difference across a resistor R, by which the collector electrode 13 is connected to the positive terminal (earth), is plotted vertically and the votage V set up between cathode 6 and anode 7 of the electron gun is plotted horizontally.

If the voltagerV has a low value, the radius of the path of electrons between the pole-pieces and hence the distance X is small. Upon increasing the voltage, X steadily increases, the ray at a given moment reaching the collector electrode 13 and rendering the latter currentconveying, so that a voltage set up across R exhibits the curve shown in Fig. 3 upon increase in voltage V The width of the apex of the curve is dependent upon the width of the electrode 13, the mutual conductance of the flanks of the curve being dependent upon the diameter of the ray of electrons and the rate at which X increases with the voltage V Owing to the particular arrangement according to the invention, it is ensured that the declined flank is extremely steep due to the ray upon leaving the collector electrode at the same time entering a range of smaller field strength and the increase of X thus becoming greater. Consequently, a great variation of V occurs upon small variation of V in this region. This fact may be utilised by comparing the voltage V with a voltage V and adding the difference between the said voltages, after amplification, to V thus enabling the voltage V with sutficient additional amplification to be stabilised at a value V Since the point P is located on a very steep portion of the curve, the value of the reference voltage V has little influence upon the voltage V The reference voltage V need not therefore be constant with great accuracy. This affords the important advantage that V may be derived with the use of a potentiometer, from a voltage stabilised by a neon discharge tube.

In one determined embodiment, the magnet poles have a base of 2 cm. and a spacing of 0.75 mm. The field strength between the poles is 800 gausses and is produced by a permanent magnet 12. The current of the ray of electrons impinging on the electrode 13 is 15 microamps. at the utmost and R=1 megohm. The voltage V is thus 15 volts at the utmost and about 7.5 volts at point P. The reference voltage V thus must also be about 7.5 volts. The voltage V is then stabilised at about 56 kilovolts, with an accuracy up to 0.05% for a long period,

and may be constant up to about 0.005% for a short period (for example 1 minute). The voltage of 56 kilovolts may thus be maintained constant at :28 volts for a long period and even at $2.8 volts during a given measurement.

In the embodiment shown in Figs. 4 and 5, it is possible for a voltage to be stabilised at different values. The magnet poles 15, 16 in this case exhibit grooves or saw cuts 20, 21, such that adjoining regions of great and small field strength occur, between which the field strength has a high gradient, since the field strength between the opposing slots is smaller than between the other parts of the pole-pieces. The pole-pieces and 16 are secured to iron plates 17, 18 between which a permanent magnet 19 is clamped in position.

The slots 20 and 21 have shapes such that the ray of electrons can extend just along the edges thereof. If the voltage of the electron gun 22 increases, the voltage set up across resistor R exhibits the curve shown in Fig. 6, stabilisation according to the invention then being ob-. tained at voltages V V V It is possible always to utilise the same reference voltage V but it is alter-. natively possible to use a different value of V for each stabilised voltage V The points P, P P" may then be provided at the centre on the strongly declined branch of 1' the curve. The collector electrodes 23, 24, 25 may be formed as a slotted plate. However, one edge of a plate or a slot is required to coincide with the corresponding edge of the pole-pieces or the slots therein, as viewed in the direction of the paths of the electrons.

The grooves constitute parts of half circles of different diameters and with the point of the base where the ray of electrons enters between the pole-pieces, as the common tangent point.

As a rule, strips of non-magnetic material 26, 27, respectively, for example of copper, must be clamped in the slots of the pole-pieces, in order that the paths of electrons remain spaced in the various stable positions, since otherwise the curves shown in Fig. 6 may form a continuous line to a certain extent. The slots each may have a depth of 1.5 mm. and a width of 1 mm., whilst the spacing between the pole-pieces may be 0.75 mm. as in the first-mentioned embodiment.

It will be evident that other embodiments according to the invention are possible. Thus, for example, a larger number of slots may be provided in the magnet poles and the collector electrodes may be connected to separate resistors. It is even possible for the collector electrodes to be arranged in such manner that, if the voltage to be stabilised increases, the current of the said electrodes increases, so that the points P come to lie on a strongly inclined branch of the curves shown in Figs. 3 and 6.

i What is claimed is:

1. An electron tube comprising means producing a beam of electrons including means for changing the velocity of the electrons in said beam by applying a voltage thereto, means establishing a magnetic field relative to the direction of said beam to thereby cause said beam of electrons having a given velocity to follow a predetermined curved path, said magnetic field-establishing means comprising a pair of spaced pole-pieces between which the field is established, said pole-pieces having opposed curved discontinuities extending parallel to said curved path and producing adjacent regions of high and low magnetic field intensity, and a collector electrode located in said curved path to intercept at least some of said electrons in said beam and in such position that a change in the curvature of said curved path followed by the beam will be manifested by a change in the quantity of electrons intercepted by said collector, whereby a change in the voltage applied to the velocity-changing means causes the beam to be subject to the adjacent magnetic field of different intensity thereby producing a substantial change in collector current in response to a relatively minor change in applied voltage.

2. A device adapted for stabilizing high yoltages com prising means producing a beam of electrons whose velocity is dependent upon the voltage to' be stabilized, means producing a magnetic field in the path of said beam and substantially at right angles thereto thereby causing said beam to follow a curved path whose curvuture is dependent upon the velocity of the electrons in the beam, a collector electrode located at the end of the curved path to intercept at least a part of said beam, said field-producing means comprising a pair of spaced, semi-- circular pole-pieces'between which the field is established and located in such manner relative to the beam that the latter enters at one end and is curved by the magnetic field to follow a path lying between the pole-pieces but adjacent the curved outer edge thereof, said collector being located at the'other end of the pole-pieces and being aligned with the curved outer edge thereof, and means coupled to the collector for deriving therefrom an elcctrical signal dependent upon the extent of electron collection by said collector, whereby an increase in the applied high voltage to the beam-producing means causes a reduction in beam curvature and a substantial change in the extent of electron collection by the collector magnifiedby the beam thereupon passing from a region of I 5 6 high field strength to the adjacent region of low field References Cited in the file of this patent sagaennlglth to thus further reduce the curvature of the UNITED STATES S V '3. A device as set forth in claim 2, in which the pole 2,161,466 Henneberg June 6, 1939 5 pieces have opposed curved grooves extending there- 5 2,213,076 Schunfiwk et g. 2 1940' along adjacent the curved path of the beam. 2,383,758 Ziebo'lz Aug; 28, 1945 4. A device as set forth in claim 3, wherein a plurality 2,442,848 Gardner June 8; 1948 of opposed grooves are present in the pole pieces, and 21 2,453,647 Van Overbeek Nov. 9, 1948 .portion of the collector is associated and aligned with 2,563,197 Sziklai et a1. Aug. 7, 1951- each opposed pair of said grooves. V 10 2,615,128 Ruderfer Oct. 21, 1952 

